Almost one million tissue allografts are transplanted each year in the United States. Approximately 700,000 bone grafts are done yearly, although it is estimated that another 300,000 patients could be helped if there were enough viable allograft bone tissue available. Transplanted skin is grafted in more than one million procedures worldwide each year, with three-quarters of this usage occurring in life-saving circumstances such as severe burns. Another 500,000 burn patients, however, could have their wound-healing time shortened if enough viable allograft skin was available from tissue banks. Similarly, corneal replacements are performed on nearly 50,000 patients each year to restore sight—another 20,000 patients, however, are turned away due to a lack of viable corneas.
A significant limitation to meeting the annual worldwide need for more tissue allografts and organs is the relative difficulty for controlling the delicate balance between the “supply” of viable explants from suitable donors and the “demand” of transplant candidates across the globe. Even in those circumstances in which suitable donor(s) and recipient(s) can be matched, another important limitation is the ability to store, screen, match, and transport tissues along the path from the site of donor harvest, to the site of the tissue storage repository, and then onward to the site of recipient transplant—a path that in many instances, may involve many days and many thousands of miles.
Perhaps the most confounding element of the migration of explanted tissues from donor to recipient is the relatively short period, post-harvest, in which the tissue or organ remains both viable, and suitable for transplantation. Unlike mammalian blood and blood components, which may be harvested and “banked” for several weeks without significant loss of viability, most explanted mammalian tissues and organs in contrast, are quite fragile. For example, the post-harvest time interval during which many human tissues remain viable (even if stored and transported under currently ideal conditions) is typically only a few days. Similarly, most mammalian organs rapidly lose viability and function after removal from the donor, and may become unsuitable for transplantation after extracorporeal storage and transport as soon as six- to eight-hours post-harvest.
Even for mammalian tissues that are most amenable to post-harvest tissue banking, the critical “window of opportunity” between harvest and transplant is only a few weeks at best. As a result, often there is not enough time to match donors and recipients, test the quality and suitability of the explant, transport the tissue from the donor to the recipient, and implant the tissue into the recipient. Consequently, there are substantially more recipients awaiting transplants than there are suitable donor tissues available for transplant.
The fact that conventional buffer solutions, physiological formulations, diluents, standard culture media, cellular growth media, tissue storage solutions, and organ transport media are typically only able to preserve the cellular viability and suitability of biological tissues or organs for transplantation for a period of a few hours to a few days post-harvest makes them largely unsuitable for prolonged- or extended-term storage of viable biological materials such as mammalian cells, tissues, organs, explants, and such like. In particular, what has been most lacking in the prior art, are compositions and methodologies that facilitate the long-term preservation of cell, tissue, and organ viability, and that maintain the biological activity, function and tissue integrity.
Moreover, what is also lacking is the ability to store such biological samples for extended periods of time, and still maintain suitability of the extended-storage product for transplanting into recipient animals, particularly when the period of time from initial harvest to ultimate transplantation in a recipient host is on the order of several weeks' to several months' duration.